Formation of fine particles with compressed gases

Abstract

The application of supercritical fluids has been introduced in the near past, especially in the field of material separation. For the large-scale production, the supercritical extraction of caffeine from raw coffee and hop with carbon dioxide as solvent was established. A new application of supercritical fluids is the formation of fine particles with a narrow particle size distribution. In this field, two different processes are available. For the RESS-process (Rapid Expansion of Supercritical Solutions), the first step is the supercritical extraction of the solid, and the second one the expansion of the loaded supercritical solution through a nozzle. The expansion causes a locally high supersaturating and thus nucleation within the free jet. Another application of supercritical fluids is their use as anti-solvent. For the GAS-process (Gas Anti-Solvent), the solid is dissolved in a common solvent. The addition of a high-compressed gas as anti-solvent results in a volumetric expansion of the solution loading to the precipitation of the solid.